CAS BI 105 Lecture Notes - Lecture 20: Homologous Chromosome, Gregor Mendel, Punnett Square
Genetics
Genetic Gambling
•For every gene that you have, you inherit 2 alleles (one from mom, one from dad)
•The of each parents’ chromosomes into gametes is random
How do our cells decide which to express?
•Gene: a sequence of DNA that controls a single functional unit (protein)
•Allele: a version of a gene
•Trait: a single characteristic (may be controlled by 1 or many genes)
Genotype
•Homo- same
•Hetero- different
•Zygo- joining “embryotic”
Haploid/ Diploid
•We have 46 chromosomes (diploid) 2 copies of each —> 23 unique chromosomes (haploid)
•Each chromosome has the same genes, but can have different alleles
•If you have the same allele on both chromosomes, you are homozygous for that allele
•If you have different alleles on the two chromosomes, you are heterozygous
Single-Gene Traits
•9,000 human traits exhibit single-gene pattern of inheritance
•When sperm + egg make a fertilized egg (egg —> fetus —> baby —> you) each gamete contributes 1
chromosome
•This results in homologous chromosomes (2 copies of each chromosome)
Homologous and Alleles
•Each homologous chromosome contains an allele of a gene
•This can result in two copies of each gene: two alleles twice or two different alleles
Recessive v. Dominant
•Dominant: protein will be made (gene is expressed)
•Recessive: protein will only be made if there is no dominant allele
Gregor Mendel
•3 ideas
•Rather than passing on the trait itself, each parent passes on instructions for building the trait
•Offspring will receive two copies of the instructions for every trait
•The trait observed depends on the set of instructions
•Led to 3 BIG ideas
•Recessive v. Dominance
•Law of Segregation
•Law of Independent Assortment
•Phenotype and Genotype
•It can be difficult to tell a genotype form the phenotype alone
•Albinism is caused by 2 recessive alleles
•ex: Is a non-albino homozygous or heterozygous for melanin pigment?
•answer: there is no melanin and no pigment so this is homozygous
Punnett Squares
•Outline the offspring that can result from two parents
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Genetic gambling: for every gene that you have, you inherit 2 alleles (one from mom, one from dad, the of each parents" chromosomes into gametes is random. How do our cells decide which to express: gene: a sequence of dna that controls a single functional unit (protein, allele: a version of a gene, trait: a single characteristic (may be controlled by 1 or many genes) Genotype: homo- same, hetero- different, zygo- joining embryotic . Homologous and alleles: each homologous chromosome contains an allele of a gene, this can result in two copies of each gene: two alleles twice or two different alleles. Recessive v. dominant: dominant: protein will be made (gene is expressed, recessive: protein will only be made if there is no dominant allele. Punnett squares: outline the offspring that can result from two parents, show all the possible gametes, autosomal-recessive traits, albinism, cystic fibrosis, hairline shape, tay sachs, rh factor on rbcs.